Innovative coating increases the efficiency and reduces the costs of solar cells
Coating solar cells with unique organic molecules could pave the way for more efficient and affordable solar panels. As reported in the journal Angewandte Chemie, this coating improves the efficiency of monolithic tandem cells made of silicon and perovskite, while reducing their costs. This is achieved by using industrial, microstructured, standard silicon wafers.
In solar cells, light excites electrons from a semiconductor, leaving positively charged “holes”. These charge carriers are separated and collected as current. Tandem cells have been developed to utilize the full spectrum of sunlight more effectively and increase the efficiency of solar cells. They are composed of two different semiconductors that absorb light of different wavelengths.
The main candidates for this technology are silicon, which mainly absorbs red and near-infrared light, and perovskite, which efficiently captures visible light. Monolithic tandem cells are made by laying these semiconductors on a support, usually using silicon wafers produced by the zone melting process with a polished or nanostructured surface. However, these waffles are expensive.
Cheaper silicon wafers produced by the Czochralski process contain micrometer-scale pyramid-shaped structural elements that improve light capture due to their lower reflectivity compared to smooth surfaces. However, coating these wafers with perovskite introduces defects in the crystal lattice, which affects the electronic properties, impedes electron transfer, and increases electron-hole recombination. This reduces both efficiency and stability.
A team led by Prof. Kai Yao of Nanchang University, in collaboration with Suzhou Maxwell Technologies, CNPC Tubular Goods Research Institute (Shaanxi), Hong Kong Polytechnic University, Wuhan University of Technology and Fudan University (Shanghai), has a surface passivation strategy to smooth out these surface defects. They use a thiophenethylammonium compound with a trifluoromethyl group (CF3-TEA), applied via a dynamic spray coating process. This forms a uniform layer even on micro-textured surfaces.
The CF3-TEA coating, due to its high polarity and binding energy, effectively reduces the effects of surface defects, suppresses non-radiative recombination and optimizes electronic levels to facilitate electron transfer to the electron-capturing layer of the solar cell. This surface modification allows perovskite/silicon tandem solar cells, based on plain textured Czochralski silicon wafers, to achieve nearly 31% efficiency and maintain long-term stability.
Research report:Surface molecular engineering for fully textured perovskite/silicon tandem solar cells
